1. Field of the Invention
The invention pertains to a valve cover for internal combustion engines in which at least one overhead camshaft is present.
2. Description of the Related Art
Valve covers for internal combustion engines, which are placed on top of an engine block and fastened there, are generally made of pressure-cast metal or shaped sheet metal. The seating for the camshafts can be at least partially formed in the process, with the actual bearings either having to be installed later or mechanically reworked.
Moreover, it possible with pressure-casting of metal to produce any arbitrary shape desired by designers, and the seating surfaces of metal covers thus produced must also be subjected to further machining.
An additional drawback of valve covers produced this way is their relatively high mass.
Valve covers produced by the metal pressure-casting method and also valve covers obtained by shaping processes achieve sound-deadening only to a limited extent and in particular solid-borne sound is easily received and shows up as an elevated noise level.
For valve covers produced by the metal pressure-casting method, it is not possible for arbitrary metals, often particularly suitable, to be used for the bearings of the camshafts.
It is therefore the problem of the invention to provide a valve cover that achieves greater design freedom, a reduced mass and improved acoustic behavior in comparison to conventional solutions.
This problem is solved according to the invention by a valve cover according to claim 1. Advantageous configurations and refinements of the invention can be achieved with the characteristics cited in the subordinate claims.
The valve cover of the invention for internal combustion engines, usually to be used in motor vehicles, is constructed such that the bearings for the one or more camshafts are embedded in a plastic material forming the valve cover.
Suitable plastic materials, which are sufficiently temperature-resistant, have resistance to attack by fuels and lubricants and achieve a sufficient strength, are well known.
The valve cover according to the invention can be produced with a high degree of design freedom by the plastic injection molding method, wherein the bearings for the camshaft or multiple camshafts are molded in at the same time and sufficiently good positioning accuracy for the camshaft bearings can be achieved with no additional effort. Since the temperatures occurring during the injection-molding of plastics are not critical, arbitrary metal bearing materials can be molded in, so that optimal bearing matching of bearings to camshaft can be achieved.
The bearings for the camshaft can be inserted into the injection mold as semifinished products and no further mechanical machining of the bearing surfaces is necessary.
The bearings for the camshafts can be constructed as bearing blocks.
To increase the stability of the bearing cover, consisting essentially of plastic material along with the appropriate bearings for the camshafts, can be increased [sic] by an additional support structure preferably consisting of metal, which is likewise embedded in the plastic material.
There are several possibilities that can be considered for the formation of such a support structure and can be used individually or in combination with one another.
Thus, such a support structure can be formed from longitudinal and/or transverse ribs which connect the bearings, even in a curved shape. The necessary strength and stability of such a support structure can be easily obtained by calculation using known methods, so that the necessary strength and stability and the increase in mass resulting from the support structure can be optimized. Thus, such a support structure can be constructed similarly to half-timbered construction [in houses].
It is also advantageous to integrate other elements necessary for valve covers into the structure of such a support structure as well. Thus, passage holes for fastening elements are necessary in any case for fastening valve covers to engine blocks to internal combustion engines; for the sake of strength in the case of a valve cover consisting essentially of plastic material, these can be imbedded and molded-in sleeve-shaped metal elements. These sleeve-shaped elements are oriented vertically and ensure a high degree of stability and strength when they are joined to other elements of the support structure and/or the bearings, so that they constitute particularly well-suited buttresses for the forces and torques that are operative.
Since the bearing points must be lubricated, the oil supply system, via channels to the respective bearing points of the camshaft(s), can also be integrated into the valve cover and corresponding oil supply channels, likewise preferably consisting of appropriately bent tubular structures, can be embedded in the plastic material and molded in during the injection-molding process. There is therefore also the possibility of integrating oil supply channels into the support structure.
There need not be any elaborate post-machining of the valve cover after removal from the injection-molding tool, apart from the removal of projecting residues of plastic and it represents a semifinished product, into which one or more camshaft(s) can be easily inserted and fixed in place.
To this end, it is possible for an opening, through which the respective camshaft can be inserted, to be present on one end face, as viewed in the longitudinal axial direction of the valve cover. The inside diameters of the bearings decrease successively starting from the insertion opening, the outer diameters of the bearing points on the camshaft decreasing to the same degree for the individual bearings arranged in succession. After the insertion of the camshaft(s) into the bearings, the insertion opening can be closed off with a metal disk affixed to the valve cover. Such a metal disk can, for instance, be fastened to the valve cover with a conventional screw closure, a corresponding threaded fitting likewise being embedded and molded into the plastic material. The metal disk can consist of a suitable metal and be correspondingly contoured so that it can simultaneously take on the functions of an axial bearing for the respective camshaft.
A continuous groove-shaped gasket receptacle arranged on the outer rim can be present on the bottom side of the valve cover, which rests on the upper end face of the engine block; a suitable gasket is inserted into [said receptacle] and positively retained there.
Such a groove-like gasket receptacle can also consist of a metal and then be partially embedded into the plastic material, so that additionally the strength and stability, as well as the accuracy of fit, are enhanced. It goes without saying that there is also the possibility of integrating such a metal gasket receptacle into the remaining support structure.
Taking into account the noise emission that occurs, the wall thickness of the plastic material being used can be of an appropriately large size at the different positions, such a design also being undertaken with consideration given to the locally differing strength requirements.
Both the strength and the acoustic behavior of the valve cover according to the invention can be increased and improved by the addition of fibers to the plastic material used. Thus, glass, plastic or carbon fibers can be employed and added to the plastic material injected into the injection molding tool, depending on the requirements.
Particularly for the small-series production of valve covers according to the invention, an appropriate fiber composite in mat or woven form can be used for reinforcement, in which case the valve covers can be manufactures with a laminate process.
In all cases, additional elements, such as a collapsible opening for adding motor oil, which are necessary for valve covers in any case, can be obtained in a single work step during the injection molding.
Furthermore, it is easily possible when using injection molding to form, on the outside of a valve cover according to the invention, receptacles for additional elements such as covers for lines or hoses which then have corresponding projections that can be pressed or screwed into the receptacles on the outside of the valve cover and retained there positively or nonpositively. Thus, the cover for a toothed belt can be correspondingly fastened to a valve cover.
The invention will be explained below in further detail on the basis of embodiments.